EFFECT OF NEUTRON IRRADIATION ON THE CRITICAL SHEAR STRESS OF A METAL SINGLE CRYSTAL
A mechanism is postulated to account for the change in the critical shear stress of a metal single crystal upon irradiation. This mechanism is based on a lattice defect consisting of interlocking dislocation rings. The dislocation rings are formed by plastic deformation of the matrix around thermal or displacement spikes in the metal, as suggested by Seitz. They remain in the lattice after irradiation to impede the movement of slip dislocations. From this model, an expression for the critical shear stress of a metal single crystal as a function of radiation dose is derived. The expression predicts that the critical shear stress varies as the cube root of the integrated neutron flux. The variation (after irradiation) of the critical shear stress with temperature ts also discussed from the standpoint of this mechanism. Other radiation-hardening mechanisms (viz., interaction of slip dislocations with interstitials and vacancies, formation of stacking faults or agglomerations of interstitials and vacancies and formation of jogs on dislocations) are discussed and the dislocation ring mechanism compared with them. The agglomerated point defect or stacking fault mechanism and the dislocation ring mechanism differ in that, while the former requires diffusion of interstitials or vacancies before the irradiated metal is hardened, the dislocation ring method predicts that metals will be hardened by radiation even at the lowest temperature without warring. To test the theory, the critical shear stress of copper was calculated for neutron doses up to 2 x 10/sup 19/ nvt. The calculated values agree quite well with available experimental data on irradiated highpurity copper crystals. Extension of the theory of polycrystalline metals and alloys is also discussed. (auth)
- Research Organization:
- Convair, Fort Worth, Tex.
- DOE Contract Number:
- AF33(600)-32054
- NSA Number:
- NSA-12-008171
- OSTI ID:
- 4343584
- Report Number(s):
- NARF-58-9T; MR-N-192; Project 6(1-9964)
- Resource Relation:
- Other Information: Project 6(1-9964). Orig. Receipt Date: 31-DEC-58
- Country of Publication:
- United States
- Language:
- English
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